Thanks to the advanced technologies and the modularized and miniaturized camera lenses, digital cameras may now have a largely reduced volume, and most of the currently available mobile phones may have a built-in digital camera to form the so-called camera phone. In the miniaturized camera lens module, an auto-focusing structure is provided. There are various types of auto-focusing structures for the modularized and miniaturized camera lens. Among others, a voice coil motor (VCM) has the advantages of small volume, low power consumption, accurately actuated displacement, and low price, and is very suitable for use as a short-distance actuator in the auto-focusing structure of the miniaturized camera lens.
FIG. 1 is an exploded perspective view of a conventional lens focusing structure used in a camera. As shown, the lens focusing structure includes a front cover 10, a rear cover 11, an outer frame 12 being provided at four inner wall surfaces with a magnet 13 each, an internally threaded lens holder 14 for a lens 15 to screw thereinto, a winding 16 wound around an outer side of the lens holder 14, and two plate springs 17 separately connected to a front and a rear end of the lens holder 14. The lens holder 14 is supported by the two plate springs 17 to axially movably locate in the outer frame 12 and be surrounded by the four magnets 13. When the winding 16 is supplied with an amount of current to thereby produce a magnetic field polarity, the lens holder 14 and the four magnets 13 mutually repulse or attract to thereby produce a push force against the lens holder 14. At this point, the lens holder 14 connected to the outer frame 12 via the plate springs 17 is allowed to displace forward until it reaches a point to focus.
An auto-focusing camera lens would inevitably jitter when the lens holder thereof is displaced to a focused point and then stopped. The jittering camera lens then gradually becomes stabilized. The amount of time required by the camera lens to go from still to moving and back to still again is referred to as dynamic response time. FIG. 2 shows a dynamic response waveform as detected from a conventional focusing structure. It can be seen from FIG. 2, the conventional focusing structure requires a considerably long time of 1.34035 seconds to go back to a still state again.
The dynamic response time has influence on the time required by a camera lens module to complete focusing, and is therefore an important factor having great influence on the quality of the camera lens module. The longer the dynamic response time is, the longer the time is required for focusing. When it is desired to effectively improve the focusing time, the dynamic response time must be shortened.
It is therefore tried by the inventor to develop a method and structure for suppressing the dynamic response time of lens focusing structure, so as to shorten or even eliminate the dynamic response time.